JP6778391B2 - Ring rolling method - Google Patents

Description

The present invention relates to a ring rolling method.

For the parts used for annular turbine discs, for example, a material made of Ni-based superheat-resistant alloy is hot-processed into a near-net shape by a ring rolling mill (also called a ring rolling mill or ring mill). ..
As a method for producing an annular product using these ring rolling mills, various proposals have been made to obtain a near-net-shaped ring-rolled material by processing the shapes of a main roll and a mandrel roll. For example, Japanese Patent Application Laid-Open No. 2013-169563 (Patent Document 1) describes ring rolling that can suppress the generation of internal voids in a product that has been ring-rolled by rolling, dividing the roll, and supplying lubricating oil. Inventions of processing methods have been proposed. Further, for example, in Japanese Patent Application Laid-Open No. 64-75134 (Patent Document 2), when rolling is performed, the ring material is rotated by applying a lubricating material to the surface of the ring material excluding the contact surface with the mandrel. An invention of a ring material manufacturing method capable of avoiding a situation in which rolling is impossible such as stopping has been proposed.

Japanese Unexamined Patent Publication No. 2013-169563 Japanese Unexamined Patent Publication No. 64-75134

As described above, in the case of ring rolling using a ring rolling mill, problems such as internal defects, external defects and rotation stoppage are being solved by supplying a lubricant.
By the way, recently, there is a demand for larger parts for aircraft and power generation, and the material is also difficult to be represented by Ni-based super heat-resistant alloys such as 718 alloys (sometimes called Fe-Ni groups). Workable alloys are used. When ring-rolling these difficult-to-process alloys, it is necessary to prevent the temperature of the rolling material for ring rolling from dropping as much as possible.
In such a case, supplying lubricating oil during ring rolling as in Patent Document 1 may lower the temperature of the rolling material for ring rolling during rolling. Further, as in Patent Document 2, there is a concern that the temperature of the ring material during rolling may decrease due to the rolling material for ring rolling coming into direct contact with the roll.

By the way, when ring rolling is performed using a large, difficult-to-process alloy as a material, it is necessary to suppress a temperature drop of the rolled material for ring rolling as much as possible. The causes of the temperature decrease include the temperature decrease due to the rolling material being carried out from the heating furnace and being allowed to cool until it is attached to the ring rolling mill, and the temperature decrease due to direct contact with the roll during ring rolling. Be done. Of these, the temperature drop of the rolled material is particularly remarkable until the rolled material is taken out from the heating furnace and attached to the ring rolling mill. No study has been made on this problem in the above-mentioned Patent Documents 1 and 2.
An object of the present invention is to provide a ring rolling method capable of ring rolling into a desired shape while suppressing a temperature drop of a rolling material for ring rolling.

According to the study of the present inventor, as a method of suppressing the temperature drop of the rolled material, a coating layer having a heat retaining effect and a lubricating effect on the surface of the rolled material in contact with the main roll or the mandrel roll and the surface of the rolled material in contact with the axial roll. It was found that it is effective to form. As for the coating layer, it is preferable to select a coating layer that does not stop the rotation of the rolled material on the surface in contact with the main roll or the mandrel roll, and the surface side in contact with the axial roll is reduced. We have found that a coating layer capable of reducing the load on the axial roll is sufficient, and have reached the present invention.

That is, in the present invention, a ring rolling mill having at least a main roll, a mandrel roll, and a pair of axial rolls is used to increase the diameter of the ring-shaped rolled material and press the height of the rolled material to press the ring. In the ring rolling method of hot rolling a rolled material, the surface in contact with the axial roll has a coating layer formed by applying or spraying a glass layer that softens at the temperature of hot rolling , and the main roll. A ring rolling method in which ring rolling is performed using a rolling material having a coating layer formed by applying or spraying a slurry-like ceramic layer that does not soften at the temperature of hot rolling on the surface in contact with the mandrel roll and the surface in contact with the mandrel roll. is there.
Further, in the present invention, the glass layer may be further coated with a sheet-shaped ceramic fiber or a heat insulating material made of glass fiber .

According to the present invention, it is possible to perform ring rolling into a desired shape while suppressing a temperature drop of a rolling material for ring rolling.

It is a perspective view for demonstrating ring rolling. It is sectional drawing which shows the relationship between the rolling material used in this invention, a main roll, a mandrel roll and an axial roll. It is one side sectional schematic diagram which shows an example of the rolling material used in this invention.

As described above, the greatest feature of the present invention is that a coating layer having a heat retaining effect and a lubricating effect is formed on the surface of the rolled material in contact with the main roll or mandrel roll and the surface of the rolled material in contact with the axial roll, and the main feature is The coating layer formed on the surface of the rolled material in contact with the roll or mandrel roll and the coating layer formed on the surface of the rolled material in contact with the axial roll are different coating layers.
On the surface of the rolled material, the surface where the main roll, the mandrel roll, and the pair of axial rolls come into contact during ring rolling is almost the entire surface. Therefore, a coating layer is formed on the surface of these rolled materials, and this coating layer functions as a heat insulating layer to carry out the rolled material from the heating furnace and allow it to cool until it is attached to the ring rolling mill. It suppresses the temperature drop due to the drop and the direct contact with the roll during ring rolling.

As a specific example, as shown in FIG. 2, a coating layer (2, 3A, 3B) is formed on the rolled material 1. FIG. 2 is a schematic view when the rolling material 1 used in the present invention is ring-rolled. The ring material is pre-processed so as to have a shape along the contact surface between the axial roll and the main roll. The shape is approximately 6 to 10 polygonal, and a coating layer 2 made of a glass layer is formed on the surface of the rolled material 1 in contact with the axial roll 13.
As shown in FIGS. 1 and 2, what is formed on the surface of the rolled material 1 in contact with the main roll 11 and the mandrel roll 12 is a coating layer (3A, 3B) made of a ceramic layer. The coating layer made of a ceramic layer enhances the heat retention function, and the rolling material 1 having a coating layer made of a ceramic layer is rolled with the main roll 11 and the mandrel roll 12 which do not soften at the temperature of hot rolling and have a low lubrication function. The material 1 is less likely to slip, and the drive of the main roll, which is driven to rotate, can be reliably transmitted to the rolled material. Therefore, it is possible to prevent the main roll 11, the mandrel roll 12, or the rolled material 1 from idling during ring rolling, and reduce the risk of causing shape defects. Among them, as the coating layer (3A, 3B), for example, one containing alumina and mica is effective from the viewpoint of heat resistance and prevention of idling. Further, in order to obtain the above effect, it is optimal that the thickness of the coating layer is 350 to 900 μm. This is because the effect is reduced when the thickness is less than 350 μm, while the coating layer is easily peeled off during rolling when the thickness is more than 900 μm.

Further, in the present invention, the coating layer 2 made of a glass layer is formed on the surface of the rolled material 1 in contact with the axial roll 13. The coating layer made of a glass layer not only enhances the heat retention function, but also has a high lubrication function because it is easily softened by the hot rolling temperature, and improves the sliding between the axial roll 13 and the rolling material 1. Unlike the relationship between the rolled material and the main roll 11 or the mandrel roll 12 described above, when the axial roll and the rolled material become excessively slippery, the axial roll becomes a resistance to rotation of the rolled material and the main roll 11 or the mandrel roll 12 or The rolled material may run idle, resulting in poor shape. The axial roll may be shaped in the axial direction (thickness direction) and can be lightly reduced, and it is not necessary to reliably follow and rotate the rotating rolled material.
Further, in the present invention, as shown in FIG. 3, the coating layer 2 made of the glass layer may be further coated with the heat insulating material 4. As the heat insulating material to be used, it is preferable to use a sheet-shaped ceramic fiber or glass fiber. There are two main purposes for coating with these insulation materials. The first purpose is to prevent a temperature drop when the rolled material heated to the ring rolling temperature is installed in the ring rolling mill. Coating layer preventing effect of the temperature drop of one layer thermal conductivity is rather low because of approximately 5 to 20 times the thickness with respect to the glass layer is obtained, the second object, by coating with a heat insulating material, glass It keeps the temperature of the layer high. By maintaining the glass layer at a high temperature, the lubricating function of the glass layer can be fully exerted. The heat insulating material 4 is arranged on the entire surface in contact with the axial roll so as to be peeled off at the initial stage of ring rolling, and after the heat insulating material 4 is peeled off, the ring rolling is performed by the lubrication function of the glass layer maintained at a high temperature. It is good to continue. As a method of coating the heat insulating material, the glass layer is reapplied and adhered to the heat insulating material.
Incidentally, "Sera mix layer" and "glass layer" is to be coated on the rolled material together with a liquid, sera mix layer has a slurry comprising ceramic particles. It is considered that the ceramic particles in the ceramic layer are crushed during ring rolling, and the lubrication performance can be lowered due to the influence of the crushed ceramic particles.

In the present invention, as a forming method for forming the above-mentioned coating layer, the coating layer is formed before the rolled material is heated to the ring rolling temperature. The coating method may be any known method such as coating or spraying. The order of coating the ceramic layer and the glass layer to be coated is not particularly limited.
The coating is performed after preheating the rolled material to 80 to 110 ° C. The purpose of this is to remove the moisture of the coating material at the moment of coating by preheating to obtain a uniform film thickness. Further, when further coating the above-mentioned heat insulating material, it is preferable to cover the glass layer with a heat insulating material having a pre-shaped shape.
The rolled material on which the coating layer is formed is put into a heating furnace heated to the ring rolling temperature and heated to a predetermined temperature. For example, in the case of a Ni-based super heat-resistant alloy such as a 718 alloy, a heating temperature of 980 to 1000 ° C. is sufficient.

Further, if the rolled material is an alloy containing Cr, when the pre-oxidation step of forming an oxide film on the rolled material in advance is applied when forming the coating layer, the adhesion between the coating layer and the rolled material is improved. improves. This pre-oxidation step is preferably performed in a temperature range of 900 ° C. to 1100 ° C. so that the Cr oxide film is continuously formed on the entire surface layer of the forging material. Below 900 ° C., it may be difficult to form a uniform Cr oxide film on the surface of the rolled material. On the other hand, the upper limit temperature of the preliminary oxidation step is the ring rolling temperature. For example, in the case of 718 alloy, it is 1000 to 1040 ° C. If the temperature of the pre-oxidation step exceeds the ring rolling temperature, the crystal grains of the material may become coarse in the pre-oxidation treatment, which is not preferable. Further, a processing time of 1 to 10 hours is sufficient.

By the way, for example, when ring rolling is performed using a large, difficult-to-process alloy having an outer diameter of 1000 mm or more and a weight of 300 kg or more as a rolling material, it is necessary to suppress a temperature drop of the rolled material as much as possible. The causes of the temperature decrease include the temperature decrease due to the rolling material being carried out from the heating furnace and being allowed to cool until it is attached to the ring rolling mill, and the temperature decrease due to direct contact with the roll during ring rolling. Be done. Of these, the temperature drop of the rolled material is particularly remarkable until the rolled material is taken out from the heating furnace and attached to the ring rolling mill.
The rolled material on which the coating layer is formed has a heat-retaining effect that prevents the temperature of the rolling material from dropping. Therefore, the temperature of the rolled material drops most severely until the rolled material is carried out from the heating furnace and attached to the ring rolling mill. It is possible to suppress the temperature drop of. Further, since it is possible to prevent the rolled material during ring rolling from coming into direct contact with the roll, it is possible to suppress a decrease in temperature of the rolled material during ring rolling. For example, if the coating layer is not formed, the temperature may drop by a hundred and several tens of degrees. On the other hand, if a coating layer is provided, the temperature can be lowered to about 70 ° C. or less, and if a heat insulating material is used, the temperature can be lowered to 50 ° C. or less.

The above-mentioned rolling material is attached to a ring rolling mill (ring mill). As the ring rolling mill used at that time, for example, as shown in FIG. 1, a ring rolling mill having at least a pair of rolling rolls including a main roll 11 and a mandrel roll 12 and at least a pair of axial rolls 13 is used. be able to. The ring rolling mill may be provided with a guide roll (holding roll) and a fixed size roll.
In the ring rolling mill shown in FIG. 1, a main roll 11 capable of rotating at a predetermined rotation speed and a mandrel roll 12 capable of driven rotation around an axis are arranged to face the radial outer peripheral surface and the inner peripheral surface of the rolling material 1. Further, this ring rolling mill is provided with two axial rolls 13 arranged to face each other on the upper surface and the lower surface of the rolling material 1 in the height direction. In order to reduce the misalignment of the rolled material 1 during ring rolling, it is more stable when a guide roll capable of driven rotation is arranged on both sides of the main roll 11 and the ring is rolled while supporting the outer peripheral portion of the rolled material 1. Ring rolling is possible.

The main roll 11 rotates the rolled material 11 by driving the rolled material 11 in contact with the outer peripheral surface of the rolled material 11 during ring rolling. The mandrel roll 12 has a structure that can freely rotate around an axis, and is arranged substantially parallel to the rotation axis of the main roll 22.
The ring rolling is performed in a state where the outer peripheral surface of the mandrel roll 12 is in contact with the inner peripheral surface of the rolling material 1. By gradually narrowing the distance between the rolls between the main roll 11 and the mandrel roll 12 during ring rolling, the portion between the radial inner peripheral surface and the outer peripheral surface of the rolled material 1 is reduced in the wall thickness direction. As a result, the diameter of the rolled material 1 can be increased.
The pair of axial rolls 13 arranged one above the other are formed in a conical shape or a truncated cone shape having an apex angle of approximately 20 to 45 °, and further, the pair of axial rolls 13 make the rolled material 1 in the height direction. In order to adjust the dimensions in the height direction by pressing the rolled material 1, the tips are arranged so as to face substantially the center of the rolled material 1. During ring rolling, the pair of axial rolls 13 are driven and rotated according to the rotation speed of the rolling material 1, but may be driven to rotate.

As a ring rolling procedure, the mandrel roll 12 is passed through the inner diameter hole of the rolled material 1 heated to a predetermined temperature, and the mandrel roll 12 is moved out of the radial direction so that the distance between the main roll 11 and the mandrel roll 12 is gradually narrowed. When the distance between the two is equal to the initial wall thickness of the rolled material 1, the rolling material 1 rotates due to friction between the surface of the main roll 11 and the outer peripheral surface of the rolled material 1. It will be granted. At this time, the mandrel roll 12 is driven to rotate so as to follow the rotation of the rolled material 1.
After that, by gradually moving the mandrel roll 12 outward (outer peripheral side) in the radial direction, the distance between the main roll 11 and the mandrel roll 12 is gradually narrowed, and the rolled material 1 is reduced in the wall thickness direction and rolled. Plastic deformation is continuously applied along the circumferential direction of the material 1.
According to the ring rolling method of the present invention described above, it is possible to stably ring roll into a desired shape while suppressing a temperature drop of the rolling material for ring rolling.

1 Rolled material 2 Coating layer (glass layer)
3A, 3B coating layer (ceramic layer)
4 Insulation material 11 Main roll 12 Mandrel roll 13 Axial roll

Claims (2)

Using a ring rolling mill having at least a main roll, a mandrel roll, and a pair of axial rolls, the diameter of the ring-shaped rolled material is increased, and the height of the rolled material is pressed to obtain a ring-shaped rolled material. In the ring rolling method of hot rolling,
The glass layer which softens at a temperature of hot rolling to the surface in contact with the axial roll has a coating layer formed by coating or spraying, and heat to the surface which contacts the surface and the mandrel roll in contact with the main roll A ring rolling method characterized by performing ring rolling using a rolling material having a coating layer formed by applying or spraying a slurry-like ceramic layer that does not soften at the temperature of inter-rolling . The ring rolling method according to claim 1, wherein the glass layer is further covered with a sheet-shaped ceramic fiber or a heat insulating material made of glass fiber .